There are several reasons to fear that if the crisis in Ukraine is not resolved diplomatically to Russia's satisfaction, Ukraine's neighbor will intervene - and some of the reasons also have to do with Syria.

Russia maintains an enormous military port in the Ukrainian city of Sevastopol, home of Russia’s mighty Black Sea Fleet. Until 1954, the port was in Russian territory, but then it was transferred to Ukraine for administrative reasons. Apparently, the Soviet leadership believed that the Soviet Union was immortal and internal administrative borders would be politically meaningless.

It became a diplomatic problem with the breakup of the Soviet Union, but a solution was found: Since 1991, the Sevastopol port has been leased to Russia, comparable to the control the Americans have of Guantanamo Bay in Cuba. Russia has another port in its territory in Novorosisk, but it is a civilian port that cannot serve as a substitute for a military port.
http://www.haaretz.com/news/world/.premium-1.576212